Wafer position teaching method and teaching jig

ABSTRACT

An object is to provide a method for teaching the position of a semiconductor wafer automatically and accurately without relying on the sight of an operator as well as a teaching jig that is used for the above method. 
     To this end, in the invention, a teaching jig  11  is detected by a first transmission-type sensor  6  that is provided at the tips of a wafer gripping portion  5  of a robot. The teaching jig  11  is composed of a large disc portion  12  that is the same in outer diameter as a semiconductor wafer and a small disc portion  13  that is concentric with the large disc portion  12 . The teaching jig  21  is detected by a second transmission-type sensor  18  that is provided on the wafer gripping portion  5 . The second transmission-type sensor  18  is mounted on a sensor jig  15  so as to be detachable form the wafer gripping portion  5.

TECHNICAL FIELD

The present invention relates to a method for teaching the position of asemiconductor wafer to a semiconductor wafer transport robot. Theinvention also relates to a teaching jig that is used for the abovemethod.

BACKGROUND ART

In semiconductor manufacturing facilities, teaching reproduction typerobots are frequently used for transport of a semiconductor waferbetween a container and a processing apparatus or between processingapparatus. Work of teaching such a robot is such that an operatormanually teaches a robot the position of a semiconductor wafer bymanipulating a teaching pendant while looking at the semiconductor waferthat is placed inside a container or the like.

Other methods are also available, examples of which are a method ofdirectly inputting the position of a semiconductor wafer on the basis ofa system drawing of semiconductor manufacturing facilities (i.e., adrawing indicating positional relationships between robots, containers,etc.) and what is called off-line teaching in which the position of asemiconductor wafer is taught while a simulation is performed on apersonal computer. However, even with those methods, it is necessary todirectly teach a robot manually for each apparatus to correct forcalibration errors of the robot itself, errors resulting from theaccuracy of finishing of each apparatus, attachment errors, etc.

Various kinds of what is called auto-teaching have been proposed inwhich a distance sensor is attached to the hand of a robot and the robotis positioned automatically by detecting a subject being transportedwith the distance sensor (e.g., Japanese Patent No. 2,898,587 andJP-A-10-6262).

However, in conventional methods, in many cases it is difficult for anoperator to approach a container or a processing device. It may bedifficult or impossible for an operator to directly see a semiconductorwafer, in which case trial-and-error attempts need to be maderepeatedly.

Since the quality of teaching work depends on the individual operator,there is a problem that variation occurs in the operation of a roboteven in the same system.

In conventional auto-teaching methods, the position of a wafer isestimated on the basis of information detected by a distance sensor thatoperates in one direction. This results in a problem that the accuracyof the direction of a wafer is not satisfactory though the distancebetween a wafer and a robot can be determined with relatively highaccuracy.

Conventional teaching jigs are composed of a large disc portion and asmall disc portion and hence are thick, which leads to a problem thatthe installation space is restricted in height.

DISCLOSURE OF THE INVENTION

An object of the present invention is therefore to provide a method forteaching the position of a semiconductor wafer automatically andaccurately without relying on the sight of an operator. Another objectof the invention is to provide a teaching jig that is used for the abovemethod.

To solve the above problems, the invention of claim 1 provides a methodfor teaching a position of a semiconductor wafer to a robot fortransporting the semiconductor wafer between a container and aprocessing apparatus or between processing apparatus, wherein a teachingjig is placed at a position of the container or the processing apparatuswhere the semiconductor wafer is to be placed, and the teaching jig isdetected by a transmission-type sensor that is provided at tips of ahand of the robot. According to the invention of claim 2, a pedestal ofthe processing apparatus on which the semiconductor wafer is to bemounted is detected by the transmission-type sensor. According to theinvention of claim 3, detection of the teaching jig or the pedestal isperformed three times or more and a position of the semiconductor waferis determined on the basis of results of the detection by aleast-squares method. According to the invention of claim 4, a teachingjig is formed by a large disc portion that is the same in outer diameteras the semiconductor wafer and a small disc portion that is concentricwith the large disc portion. According to the invention of claim 5, apin is provided approximately at a center axis position of the teachingjig and a second transmission-type sensor is provided on the hand, andthe wafer position teaching method comprises a first step of determininga height of the teaching jig by detecting an outer circumference of theteaching jig with the first transmission-type jig; a second step ofdetermining a position of the pin by detecting the pin with the firsttransmission-type sensor; and a third step of determining a position ofthe pin by detecting the pin with the second transmission-type sensor bycausing the second transmission-type sensor to approach the pin on thebasis of the position of the pin determined by the second step.According to the invention of claim 6, the second transmission-typesensor is mounted on a sensor jig so as to be detachable from the hand.According to the invention of claim 7, the second transmission-typesensor is disposed approximately at the center of a semiconductor wafermounting portion of the hand. According to the invention of claim 8, anoptical axis of the second transmission-type sensor is set approximatelyperpendicular to an optical axis of the first transmission-type sensor.According to the invention of claim 9, the sensor jig is formed with acut for preventing interference with the optical axis of the firsttransmission-type sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a robot that is used in practicing the presentinvention;

FIG. 2 is another plan view of the robot;

FIG. 3 is a side view of the robot;

FIG. 4 illustrates a transmission-type sensor according to a firstembodiment of the invention;

FIGS. 5-7 illustrate a wafer position teaching method according to theinvention;

FIG. 8 and 9 are plan views of sensor jigs according to a secondembodiment of the invention;

FIG. 10 illustrates a wafer position teaching method according to thesecond embodiment of the invention;

FIG. 11 is a flowchart showing a processing procedure of a waferposition teaching method according to the second embodiment of theinvention; and

FIGS. 12 and 13 illustrate the wafer position teaching method accordingto the second embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be hereinafter describedwith reference to the drawings. FIGS. 1 and 2 are plan views of a robotaccording to the embodiment of the invention. FIG. 3 is its side view.

In these figures, reference numeral 1 denotes a horizontal multi-jointrobot for semiconductor wafer transport and character W denotes asemiconductor wafer as a subject to be transported by the robot 1. Therobot 1 is equipped with a first arm 3 that is swung in a horizontalplane about a center axis 7 of a cylindrical prop 2 that can be elevatedand lowered, a second arm 4 that is attached to the tip of the first arm3 so as to be able to swing in a horizontal plane, and a wafer grippingportion 5 that is attached to the tip of the second arm 4 so as to beable to swing in a horizontal plane. The wafer gripping portion 5 aY-shaped hand on which the semiconductor wafer W can be mounted. Thewafer gripping portion 5 has a first transmission-type sensor 6 at thetips of the Y shape.

As shown in the figures, the robot 1 has three degrees of freedom: aθ-axis operation (circling) in which the first arm 3 is swung about thecenter axis 7 of the prop 2 while the angles between the first arm 3,the second arm 4, and the wafer gripping portion 5 are maintained; anR-axis operation (expansion/contraction) in which the wafer grippingportion 5 is advanced or retreated in a radial direction of the prop 2;and a Z-axis operation (elevation/lowering) in which the prop 2 iselevated or lowered.

The plus direction of the θ-axis is set to the counterclockwisedirection (see FIG. 1), the plus direction of the R-axis is set to thedirection in which the wafer gripping portion 5 goes away from the prop2 (see FIG. 2), and the plus direction of the Z-axis is set to thedirection in which the prop 2 is elevated (see FIG. 3).

FIG. 4 illustrates a transmission-type sensor according to theembodiment of the invention. In the figure, reference numeral 8 denotesa light-emitting portion that is attached to one end of the Y-shapedwafer gripping portion 5 and numeral 9 denotes a light-receiving portionthat is attached to the other end so as to be opposed to thelight-emitting portion 8. The light-emitting portion 8 and the lightreceiving portion 9 constitute the first transmission-type sensor 6.Reference numeral 10 denotes an optical axis that extends from thelight-emitting portion 8 to the light-receiving portion 9. The firsttransmission-type sensor 6 can detect an object that intersects theoptical axis 10.

FIGS. 5 and 6 illustrate a wafer position teaching method according tothe embodiment of the invention. In these figures, reference numeral 11denotes a teaching jig in which a large disc portion 12 and a small discportion 13 are laid one on the other concentrically in the verticaldirection and combined together. The large disc portion 12 is the samein diameter as a real semiconductor wafer, and can be placed at aposition of a container or the like where a semiconductor wafer is to beplaced. Since the relative positional relationship between the largedisc portion 12 and the small disc portion 13 is measured in advance,the position of the large disc portion 12 can be recognized byrecognizing the position of the small disc portion 13.

The thickness of the large disc portion 12 is about 2 mm and is greaterthat that (0.7 mm) of the real semiconductor wafer, and this isdetermined from strength-related restrictions. It goes without sayingthat it is desirable that the thickness of the large disc portion 12 bethe same as that of the real semiconductor wafer.

Next, the procedure of the wafer position teaching method will bedescribed.

(Step 1) The teaching jig 11 is placed at a position of a container orthe like where a semiconductor wafer is to be placed. Since the largedisc portion 12 is completely the same in outer diameter as the realsemiconductor wafer, the large disc portion 12 is positioned correctlyby positioning guides or the like of the container or the like.

(Step 2) As a result of a manipulation by an operator, as shown in FIG.6, the wafer gripping portion 5 is moved to above the small disc portion13.

(Step 3) The wafer gripping portion 5 is lowered, and the top surface ofthe small disc portion 13 is detected by the first transmission-typesensor 6. A Z-axis coordinate Z1 of the robot 1 in this state isrecorded. The wafer gripping portion 5 is further lowered, and thebottom surface of the small disc portion 13 is detected by the firsttransmission-type sensor 6. A Z-axis coordinate Z2 of the robot 1 inthis state is recorded.

(Step 4) The Z-axis coordinate of the robot 1 is set at (Z1+Z2)/2; thatis, the height of the wafer gripping portion 5 is set at the center ofthe top surface and the bottom surface of the small disc portion 13.

(Step 5) An R-axis operation is performed so that the arms arecontracted to such an extent that the first transmission-type sensor 6comes not to detect the small disc portion 13.

(Step 6) A θ-axis operation is performed so as to change the directionthe wafer gripping portion 5 points to. Then, an R-axis operation isperformed so that the wafer gripping portion 5 approaches the small discportion 13 slowly. And θ-axis and R-axis coordinates that are obtainedwhen: the first transmission-type sensor 6 first detects the small discportion 13 (i.e., the optical axis 10 comes into contact with thecircumferential surface of the small disc portion 13) are recorded.

(Step 7) Steps 6 and 7 are executed repeatedly. That is, the wafergripping portion 5 is caused to approach the small disc portion 13 indifferent directions. Plural sets of θ-axis and R-axis coordinates areobtained when the optical axis 10 comes into contact with thecircumferential surface of the small disc portion 13. The position ofthe center of the small disc portion 13 is determined on the basis ofthese values and recorded.

The position of the small disc portion 13 is determined in the abovemanner. Since the relative positional relationship between the smalldisc portion 13 and the large disc portion 12 is measured in advance,the position of the large disc portion 13, that is, the position of asemiconductor wafer to be mounted on the container or the like, can bedetermined by shifting the position of the small disc portion 13 by alength of the positional relationship.

If the operations of steps 2 to 7 are programmed in advance, theteaching of the position of the semiconductor wafer can be performedautomatically without any manipulations by an operator.

Where the processing apparatus to teach is an apparatus such as apre-aligner for mounting a semiconductor wafer on a disc-shapedpedestal, it is possible to teach the apparatus the position of thesemiconductor wafer by executing steps 1 to 7 on the pedestal instead ofthe small disc portion 13 of the teaching jig 11.

Next, the procedure of calculations for determining center coordinates(θs, Rs) of the small disc portion 13 at steps 2 to 7 will be describedin detail. FIG. 7 illustrates a state that the optical axis 10 is incontact with the circumferential surface of the small disc portion 13.Parameters θi and Ri represent θ-axis and R-axis coordinates of therobot 1 in a state that the optical axis 10 of the firsttransmission-type sensor 6 is in contact with the circumferentialsurface of the small disc portion 13. The following equation holds:Ri+r=(Rm+r)*cos(θi−θs)  (1)where Rm represents a distance between the contact point of the opticalaxis 10 and the circumferential surface of the small disc portion 13 andthe rotation center of the first arm 3, and r represents the radius ofthe small disc portion 13.

Since Rs=Rm+r,Ri+r=Rs*cos(θi−θs)  (2)Modifying Equation (2), we obtainRi+r=Rs*cos θs*cos θi+Rs*sin θs*sin θi  (3)Substituting A=Rs*cos θs and B=Rs*sin θs into Equation (3), we obtainthe following equation:Ri+r=A*cos θi+B*sin θi  (4)

In this state, as described above for step 7, measurements are performedrepeatedly while the direction the wafer gripping portion 5 points to ischanged. Three or more sets of θi and Ri values are obtained, and thecoefficients A and B are determined by the least-squares method.

Once the coefficients A and B are determined, θs is given byθs=tan⁻¹(B/A).  (5)Since cos θs=A/√{square root over ( )}(A²+B²), Rs is given byRs=√{square root over ( )}(A ² +B ²).  (6)

Next, a second specific embodiment of the invention will be described.

FIG. 8 is a plan view of a sensor jig 14 that is used in practicing theinvention. Reference numeral 15 denotes a sensor mount plate, which is aflat plate obtained by forming a V-shaped cut in a disc and has fourpositioning holes 16. The positioning holes 16 are guide holes forcorrectly positioning the sensor jig 14 with respect to a wafer grippingportion (described later) via positioning pins of the: wafer grippingportion. The above-mentioned V-shaped cut is a sensing cut 17, which isto prevent the sensor mount plate 15 from interfering with the opticalaxis of a first transmission-type sensor of the wafer gripping portionwhen the sensor jig 14 is attached to the wafer gripping portion or frominterfering with a pin of a teaching jig (described later). Referencenumeral 18 denotes a second transmission-type sensor that is fixed tothe sensor mount plate 15 at the center. Reference numeral 19, denotesthe optical axis of the second transmission-type sensor 18. The secondtransmission-type sensor 18 is generally shaped like a bracket, and thewidth of its opening, that is, the length of the optical axis 19, isabout 13 mm. Since the second transmission-type sensor 18 is fixed tothe sensor mount plate 15 at the center, the second transmission-typesensor is located approximately at the center of a semiconductormounting portion of a robot hand when the sensor jig 14 is attached tothe robot hand. Reference numeral 20 denotes a sensor cable for sendinga signal of the second transmission-type sensor to a robot controller(not shown).

FIG. 9 is a plan view of another sensor jig 14. This sensor jig 14 ischaracterized in that the sensing cut 17 of the sensor mount plate 15 isshaped so as to have a minimum necessary size and that peripheral partsof the sensor mount plate 15 are cutaway. In the other points, theconfiguration and the functions of this sensor jig 14 are the same asthose of the sensor jig 14 of FIG. 8.

Next, a wafer position teaching method using the above sensing jig willbe described, FIG. 10 illustrates a wafer position teaching methodaccording to the second embodiment of the invention and shows a statethat the sensing jig 114 is attached to a robot wafer gripping portion 5and brought in close proximity to a teaching jig 21. The robot wafergripping portion 5 is the same as the one described in the firstembodiment except that the former is equipped with positioning pins 22and a sensor cable connector 23. The positioning pins 22 are guide pinsto fit into the positioning holes (not shown in this figure) of thesensor mount plate 15 and to correctly position the sensor jig 14 withrespect to the robot wafer gripping portion 5. The sensor cableconnector 23 is a connector to which the sensor cable 20 is connected.

Where as the optical axis 10 of the first transmission-type sensor 6that is fixed to the robot wafer gripping portion 5 is perpendicular tothe length axis of the robot wafer gripping portion 5, the optical axis19 of the second transmission-type sensor 18 that is fixed to thesensing jig 14 is set parallel with the above length axis. That is, theoptical axes 10 and 19 are perpendicular to each other. The teaching jig21 is such that a small-diameter pin 24 erects from the center of thelarge disc portion 12 that is the same in diameter as the realsemiconductor wafer. The large disc portion 12 can be placed at aposition of a container or the like where a semiconductor wafer is to beplaced. The diameter of the small-diameter pin 24 is about 3 mm. Thisdiameter value is determined so as to provide a sufficient margin withrespect to the width 13 mm of: the opening of the secondtransmission-type sensor 18. Since the relative positional relationshipbetween the large disc portion 12 and the small-diameter pin 24 ismeasured in advance, the position of the large disc portion 12 can berecognized by recognizing the position of the small-diameter pin 24.

The thickness of the large disc portion 12 is about 2 mm and is greaterthat that (0.7 mm) of the real semiconductor wafer, and this is relatingto the strength. It goes without saying that it is desirable that thethickness of the large disc portion 12 be the same as that of the realsemiconductor wafer.

FIG. 11 shows a processing procedure of the wafer position teachingmethod according to the second embodiment of the invention. Thisprocessing procedure will be described below step by step.

(Step 1) The sensor jig 14 is mounted on the wafer gripping portion 5 ofthe robot in such a manner as to be positioned correctly with respect toeach other by using the positioning holes 16 and the positioning pins22. The sensor cable 20 is connected to the connector 23.

(Step 2) The teaching jig 21 is placed at a position of a container orthe like where a semiconductor wafer is to be placed. Since the largedisc portion 12 of the teaching jig 21 is completely the same in outerdiameter as the real semiconductor wafer, the teaching jig 21 ispositioned correctly by positioning guides or the like of the containeror the like.

(Step 3) As a result of a manipulation by an operator, as shown in FIG.12, the wafer gripping portion 5 is moved to below the large discportion 12.

(Step 4) The wafer gripping portion 5 is elevated, and the bottomsurface of the large disc portion 12 is detected by the firsttransmission-type sensor 6. A Z-axis coordinate Z₁ of the robot in thisstate is recorded. The wafer gripping portion 5 is further elevated, andthe top surface of the large disc portion 12 is detected by the firsttransmission-type sensor 6. A Z-axis coordinate Z₂ of the robot in thisstate is recorded.

(Step 5) The above the large disc portion 12. That is, the wafergripping portion 5 is moved to a height where the firsttransmission-type sensor 6 will be able to detect the small-diameter pin24 when the wafer gripping portion 5 is advanced (here, the advancementis in the positive direction of the R-axis).

(Step 6) The wafer gripping portion 5 is retreated to a position wherethe first transmission-type sensor 6 does not detect the small-diameterpin 24.

(Step 7) A θ-axis operation is performed so as to change the directionthe wafer gripping portion 5 points to. Then, an R-axis operation isperformed so that the wafer gripping portion 5 advances and approachesthe small-diameter pin 24 slowly. And θ-axis and R-axis coordinates thatare obtained when the first transmission-type sensor 6 first detects thesmall-diameter pin 24 (i.e., the optical axis 10 comes into contact withthe circumferential surface of the small-diameter pin 24) are recorded.

(Step 8) Steps 6 and 7 are executed repeatedly. That is, the wafergripping portion 5 is caused to approach the small-diameter pin 24 indifferent directions. Plural sets of θ-axis and R-axis coordinates areobtained when the optical axis 10 comes into contact with thecircumferential surface of the small-diameter pin 24. The position (θs,Rs) of the center of the small-diameter pin 24 is determined on thebasis of these values by the least-squares method and is recorded.

(Step 9) θ-axis and R-axis operations are performed on the basis of theposition of the small-diameter pin 24 determined by step 8, whereby thewafer gripping portion 5 is moved to the position shown in FIG. 13.Since the dimensions of the sensor mount plate 15, the sensing cut 17,and the second transmission-type sensor 18 are measured in advance, thewafer gripping portion 5 can be moved to the position shown in FIG. 13without causing interference with the small-diameter pin 24.

(Step 10) A θ-axis operation is performed, whereby the optical axis 19of the second transmission-type sensor 18 is caused approach thesmall-diameter pin 24 slowly. A θ-axis coordinate θ₁ that is obtainedwhen the second transmission-type sensor 18 first detects thesmall-diameter pin 24 (i.e., the optical axis 19 comes into contact withthe right side surface of the small-diameter pin 24) is recorded. Then,a θ-axis coordinate θ₂ that is obtained when the secondtransmission-type sensor 18 comes not to detect the small-diameter pin24 (i.e., the optical axis 19 is separated from the left side surface ofthe small-diameter pin 24) is recorded.

As for the estimate position of the small-diameter pin 24, (Z₁+Z₂)/2that is calculated from Z₁ and Z₂ that were stored at step 4, Rs thatwas determined at step 8, and (θ₁+θ₂)/2 that is calculated from θ₁ andθ₂ that were stored at step 10 are stored as a Z-axis estimate value, anR-axis estimate value, and a θ-axis estimate value, respectively.

The position of the small-diameter pin 24 is determined in theabove-described manner. Since the relative positional relationshipbetween the small-diameter pin 24 and the large disc portion 12 ismeasured in advance, the position of the large disc portion 13, that is,the position of a semiconductor wafer to be mounted on the container orthe like, can be determined by shifting the position of thesmall-diameter pin 24 by a length of the positional relationship.

If the operations of steps 3 to 10 are programmed in advance, theteaching of the position of the semiconductor wafer can be performedautomatically without any manipulations by an operator.

The manner of deriving θs and Rs by the least-squares method at step 8is not described here because it was described in the first embodiment.

In this embodiment, the positioning holes 16 and the positioning pins 22are used to position the sensor jig 14 with respect to the wafergripping portion 5 of the robot. However, if the diameter of the sensormount plate 15 is made the same as that of the semiconductor wafer to betransported, the sensor jig 14 can be positioned automatically by thefunction of the gripping mechanism of the wafer gripping portion 5itself. This manner of positioning may be employed. Other means may beemployed as long as they can correctly position the sensor jig 14 withrespect to the wafer gripping portion 5 of the robot.

As described above, according to the invention of claim 1, the teachingjig is detected by the transmission-type sensor that is attached to thewafer gripping portion. Since a position of a semiconductor wafer can betaught automatically, correct teaching can be attained even if thesemiconductor wafer is located at such a position as not be seendirectly by an operator. Another advantage is that teaching results ofconstant quality can be obtained irrespective of the skill of theoperator.

According to the invention of claim 2, the position of a semiconductorwafer is taught by detecting the pedestal of a processing apparatus onwhich the semiconductor wafer is to be mounted. This provides anadvantage that the invention can be practiced at a low cost because nospecial jig is needed.

According to the invention of claim 3, a measurement is performed pluraltimes and a position of the semiconductor wafer is determined by theleast-squares method. This provides an advantage that the position of asemiconductor wafer can be taught more accurately.

The teaching jig according to the invention of claim 4 a teaching jighas the large disc portion that is the same in outer diameter as thereal semiconductor wafer. This provides an advantage that the teachingjig can correctly be mounted on a container or the like and hence theaccuracy of position teaching can be increased.

According to the invention of claim 5, a small-diameter pin is senseddirectly. This provides an advantage that the accuracy of positionteaching relating to the θ-axis can be increased.

According to the inventions of claims 6 and 7, the secondtransmission-type sensor is disposed approximately at the center of thesemiconductor wafer mounting portion of the robot hand. Therefore,position teaching can be performed in a posture that is close to aposture that is assumed in mounting a wafer actually. This provides anadvantage that the accuracy of position teaching relating to the θ-axiscan be increased even in the case where the accuracy of relativemovement of the robot is low.

According to the invention of claim 8, the optical axis of the secondtransmission-type sensor can be set approximately perpendicular to theoptical axis of the first transmission-type sensor. This provides anadvantage that the accuracy of position teaching relating to the θ-axiscan be increased

According to the invention of claim 9, there is no interference in ahorizontal plane between the sensor jig and the small-diameter pin.Therefore, the second transmission-type sensor can be caused to approachthe small-diameter pin only by R-axis and θ-axis operations. Thisprovides an ad-vantage that a wafer position can be taught automaticallyeven in a space having only a small margin in the vertical direction(i.e., Z-axis direction).

INDUSTRIAL APPLICABILITY

The invention is useful as a method for teaching the position of asemiconductor wafer to a semiconductor wafer transport robot. Theinvention also useful as a teaching jig that is used for the abovemethod.

[FIG. 1]

-   1: ROBOT-   2: PROP-   3: FIRST ARM-   4: SECOND ARM-   5: WAFER GRIPPING PORTION-   6: TRANSMISSION-TYPE SENSOR-   A: θ-AXIS-   B: +DIRECTION    [FIG 2]-   A: R-AXIS-   B: +DIRECTION    [FIG. 3]-   A: Z-AXIS-   B: +DIRECTION-   C: θ-AXIS    [FIG. 4]-   6: TRANSMISSION-TYPE SENSOR-   8: LIGHT-EMITTING PORTION-   9: LIGHT-RECEIVING PORTION    [FIG: 5]-   10: OPTICAL AXIS-   11: TEACHING JIG-   12: LARGE DISC PORTION-   13: SMALL DISC PORTION    [FIG. 8]-   14: SENSOR JIG-   15: SENSOR MOUNT PLATE-   16: POSITIONING HOLE-   17: SENSING CUT-   18: SECOND TRANSMISSION-TYPE SENSOR-   20: SENSOR CABLE    [FIG. 10]-   21: TEACHING JIG-2-   22: POSITIONING PIN-   23: SENSOR CABLE CONNECTOR-   24: SMALL-DIAMETER PIN    [FIG. 11]-   STEP 1: MOUNT TRANSMISSION-TYPE SENSOR UNIT-2 ON WAFER GRIPPING    PORTION OF ROBOT.-   STEP 2: SET TEACHING JIG.-   STEP 3: MOVE WAFER GRIPPING PORTION TO BELOW LARGE DISC PORTION.-   STEP 4: DETECT BOTTOM SURFACE AND TOP SURFACE OF SMALL DISC PORTION    WHILE ELEVATING WAFER GRIPPING PORTION, AND RECORD Z-AXIS    COORDINATES Z₁ AND Z₂.-   STEP 5: MOVE WAFER GRIPPING PORTION TO HEIGHT WHERE SMALL-DIAMETER    PIN CAN BE DETECTED.-   STEP 6: PERFORM R-AXIS OPERATION TO RETREAT WAFER GRIPPING PORTION    TO POSITION WHERE SENSOR DOES NOT DETECT SMALL-DIAMETER PIN.-   STEP 7: PERFORM θ-AXIS OPERATION TO CHANGE DIRECTION WAFER GRIPPING    PORTION POINTS TO. PERFORM R-AXIS OPERATION TO CAUSE WAFER GRIPPING    PORTION TO APPROACH SMALL-DIAMETER PIN SLOWLY. RECORD θ-AXIS AND    R-AXIS COORDINATES THAT ARE OBTAINED WHEN SENSOR DETECTS SMALL DISC    PORTION.    HAVE STEPS 6 AND 7 BEEN EXECUTED N TIMES?-   STEP 8: DETERMINE CENTER POSITION OF SMALL DISC PORTION BY    LEAST-SQUARES METHOD ON THE BASIS OF VALUES RECORDED AT STEPS 6 AND    7, AND RECORD CENTER POSITION.-   STEP 9: PERFORM θ-AXIS AND R-AXIS OPERATIONS ON THE BASIS OF    POSITION OF SMALL DIAMETER PIN DETERMINED AT STEP 8, TO THEREBY MOVE    WAFER GRIPPING PORTION TO POSITION OF FIG. 13.-   STEP 10: PERFORM θ-AXIS OPERATION IN POSITIVE DIRECTION, AND RECORD    θ-AXIS COORDINATES θ₁ AND θ₂ THAT AE OBTAINED WHEN SENSOR-2 CONTACTS    RIGHT SIDE SURFACE OF SMALL-DIAMETER PIN AND WHEN IT SEPARATES FROM    LEFT SIDE SURFACE OF SMALL-DIAMETER PIN.

1. A wafer position teaching method for teaching a position of asemiconductor wafer in a container or a processing apparatus to a robotfor transporting the semiconductor wafer between the container and theprocessing apparatus or between processing apparatuses by moving a handholding the semiconductor wafer in at least three directions of R, θ andZ, the method comprising the steps of: placing a first teaching jig at aposition to which the semiconductor wafer in the container or theprocessing apparatus is placed, wherein the teaching jig comprises alarge disc portion and a small disc portion connected to each other withthe small disc portion overlapping the large disc portion and the largedisc portion having a diameter same as a diameter of the semiconductorwafer; detecting a height of the small disc portion by a firsttransmission-type sensor provided at tips of the hand by moving the handin the Z-direction, detecting the small disc portion by the firsttransmission-type sensor by moving the hand in the R-direction fromplural values of θ; and calculating a position of the small disc portionon the basis of the detection.
 2. The wafer position teaching methodaccording to claim 1, wherein a least-squares method is applied toresults of detection.
 3. The wafer position teaching method according toclaim 1 wherein in the step of placing the first teaching jig, the largedisc portion and the small disc portion are concentric with each other.4. A wafer position teaching method for teaching a position of asemiconductor wafer in a container or a processing apparatus to a robotfor transporting the semiconductor wafer between the container and theprocessing apparatus or between processing apparatuses by moving a handholding the semiconductor wafer in at least three directions of R, θ andZ, the method comprising the steps of: placing a sensor jig to which asecond transmission-type sensor is fixed to the hand of which tips areprovided with the first transmission-type sensor, placing a secondteaching jig at a position to which the semiconductor wafer in thecontainer or the processing apparatus is placed, wherein the secondteaching jig comprises a large disc portion having a diameter same as adiameter of the semiconductor wafer and a small diameter pin that erectsfrom a center of the large disc portion, detecting a height of the largedisc portion by the first transmission-type sensor by moving the hand inthe Z-direction, detecting the small-diameter pin by a firsttransmission-type sensor by moving the hand in the R-direction from aplural values of θ; and calculating a position of the small-diameter pinon the basis of detection.
 5. The wafer position teaching methodaccording to claim 4, wherein in the step of placing the sensor jig, anoptical axis of the second transmission-type sensor is disposedapproximately at the center of the sensor jig.
 6. The wafer positionteaching method according to claim 4, wherein in the step of placing thesensor jig, an optical axis of the second transmission-type sensor isset approximately perpendicular to an optical axis of the firsttransmission-type sensor.
 7. The wafer position teaching methodaccording to claim 5, wherein the second transmission-type sensor isdisposed approximately at the center of a semiconductor wafer mountingportion of the hand.
 8. The wafer position teaching method according toclaim 5, wherein an optical axis of the second transmission-type sensoris set approximately perpendicular to an optical axis of the firsttransmission-type sensor.
 9. The wafer position teaching methodaccording to claim 6, wherein the sensor jig is formed with a cut forpreventing interference with an optical axis of the firsttransmission-type sensor.